Poly Tetra Fluro Ethylene vs Native Collagen Membrane for Gbr in Anterior Maxilla

The alveolar bone is formed during tooth eruption, and consists of maxillary and mandibular components that shape and support the alveolar sockets. When teeth are lost, alveolar atrophy occurs, ultimately resulting in a short and narrow alveolar ridge . Such changes in the alveolar bone have a significant effect on prosthetic restoration planning, and are particularly important for areas with esthetic requirements, such as the maxillary incisors. Since preservation of the alveolar bone after extraction makes implant placement and prosthetic restoration easier in the edentulous jaw, alveolar ridge preservation and reconstruction methods using various bone graft materials together with resorbable and non-resorbable membranes have been introduced in order to minimize the loss of alveolar bone after extraction.

Investigations of changes in the alveolar bone after extraction have frequently been performed through clinical measurements and radiographic analysis. In particular, after the extraction of a tooth with fracture or severe periodontitis, the alveolar bone shows severe horizontal and vertical atrophy. The reduction in the width of the alveolar ridge is more notable in the horizontal direction than in the vertical direction, and the buccal wall of the alveolar bone has been reported to undergo greater vertical atrophy than the lingual wall. Changes in the width of the alveolar ridge after extraction occur in a relatively short time, decreasing most rapidly within the first six months after extraction, followed by continual, slow bone resorption over the course of the rest of the patient's life .

When a tooth has been lost, the extent of alveolar bone resorption is affected by a range of factors, including the number of extracted teeth and bone walls, the bone density, the extent of alveolar bone loss, infection, and the presence or absence of adjacent teeth.

Dental implant has become a predictable treatment option, with excellent long-term results. However, the success of implant therapy depends on the amount of bone volume at the insertion site.Unfavorable local conditions may provide insufficient bone volume that negatively affects the prognosis of dental implants. Cawood and Howell in 1988 ranked the atrophy degree of edentulous jaws in six classes. Particularly, atrophies within class IV, also known as "knife-edge" ridges, present a serious horizontal defect, making challenging the placement of regular implants.

Many techniques have been developed to regenerate atrophic alveolar jaws for the placement of dental implants, performed either in combination with graft procedures or in second stage surgery after a period of healing. For many years, bone blocks represented the gold standard to reconstruct the alveolar ridge bone defects. This technique requires to harvest a wide amount of bone to rebuild the atrophic crest.(20). For this reason, bone blocks were often harvested from extra-oral sites with an higher morbidity. Moreover some problems can occur when a combined defects (horizontal and vertical) need to be treated. Guided bone regeneration (GBR) has been proposed as a possible alternative for patients with severe horizontal bone atrophy, to overcome the drawback of bone blocks techniques. To protect and prevent the invasion of the clot by nonosteogenic cells, maintaining an adequate biological space for the regeneration of bone tissue, the use of both non-resorbable or resorbable membranes, in combination with autologous or heterologous particulate bone have been proposed. Particulated autogenous bone can be mixed with bone substitutes to add more osteogenic factors.

Guided bone regeneration or GBR, and guided tissue regeneration or GTR are dental surgical procedures that use barrier membranes to direct the growth of new bone and gingival tissue at sites with insufficient volumes or dimensions of bone or gingiva for proper function, esthetics or prosthetic restoration.

GBR is similar to guided tissue regeneration (GTR) but is focused on development of hard tissues in addition to the soft tissues of the periodontal attachment. At present, guided bone regeneration is predominantly applied in the oral cavity to support new hard tissue growth on an alveolar ridge to allow stable placement of dental implants.

The first application of barrier membranes in the mouth occurred in 1982. in the context of regeneration of periodontal tissues via GTR, as an alternative to resective surgical procedures to reduce pocket depths.Barrier membrane is utilized in GBR technique to cover the bone defect and create a secluded space, which prevents the connective tissue from growing into the space and facilitates the growth priority of bone tissue.

Several surgical techniques via GBR have been proposed regarding the tri-dimensional bone reconstruction of the severely resorbed maxilla, using different types of bone substitutes that have regenerative, osseoinductive or osseoconductive properties which is then packed into the bony defect and covered by resorbable membranes. In cases where augmentation materials used are autografts or allografts the bone density is quite low and resorption of the grafted site in these cases can reach up to 30% of original volume. For higher predictability, nonresorbable titanium-reinforced d-polytetrafluoroethylene (d-PTFE) membranes-as a barrier against the migration of epithelial cells within the grafted site-are recommended.

Non-resorbable membranes retain their shape and structure in the tissues, requiring a second surgical procedure for removal, with consequent additional patient discomfort, and a raise in the costs and duration of the therapy. Non-resorbable membranes include: (i) expanded polytetrafluoroethylene (e-PTFE, Gore-Tex®); (ii) high-density polytetrafluoroethylene (d-PTFE) and (iii) titanium-reinforced expanded polytetrafluoroethylene (Ti-e-PTFE) membranes. The PTFE physico-chemical, thermal, and mechanical properties make it one of the most inert materials.The microstructure of e-PTFE consists of solid nodes interconnected by fine, highly oriented fibrils, providing a unique porous structure. The e-PTFE membranes, first used in 1984, have different structural features at both membrane sides.Effectiveness of e-PTFE membranes was investigated in numerous clinical studies, that confirmed their excellent biocompatibility, leading to a significant bone regeneration after 3- and 6-month healing period .However, drawbacks of e-PTFE membranes are (i) the need for a second surgical procedure and (ii) membrane stiffness that may result in soft tissue dehiscence (which is the cause of failure during the first 3 weeks after membrane implantation), allowing the exposure of the membrane to bacterial infection.

The d-PTFE membrane, developed in 1993, is a non-resorbable membrane, consisting of a high-density PTFE having submicron (0.2 μm) pores. The d-PTFE membranes do not require primary closure and preserve the full width of keratinized mucosa, producing an interesting advantage in respect to e-PTFE. Compared to e-PTFE membranes, the macroporosity of which enhances bacterial colonization upon exposure .the density of the d-PTFE membranes (i) prevents the infections as widely described by different authors .and (ii) makes membranes easy to be removed.

Titanium-reinforced barrier membranes were introduced (Cytoplast® TI-250 Titanium-Reinforced) by Jovanovic and Nevins . who reported the superior regenerative ability of these membranes in respect to the conventional e-PTFE ones. The titanium reinforcement provides mechanical support to the overlying soft tissue preventing its collapse into the defect. In addition, during the surgical procedure, titanium struts permit the surgeon to easily place the membrane under flaps with minimal dissection and flap reflection Native collagen membranes have rapid biodegradation by the enzymatic activity of macrophages and polymorphonuclear leucocytes occurs when using them. these membranes are well documented and have excellent results . they have good tissue integration and vascularization from periosteal side.there is a debate about what is more important biocompatibility or resorption time . The most important commercial collagen membrane is Bio-Gide®, which is based on Xenogenic collagen Type I form porcine skin and is characterized by a bilayered structure with a dense and a porous layer. The dense layer has a smooth surface able to avoid epithelial cell infiltration into bone defects, while the porous layer allows tissue integration.